1. Field of the Invention
The present invention relates to the art of railway cab signalling pick-up sensors. More particularly, the invention relates to a device mounted on a railway locomotive axle to detect signalling information transmitted through the axle.
2. Description of the Prior Art
Traditionally, railway signalling has been provided by wayside indicators such as lights. The indicators alert the locomotive engineer of potential dangers ahead. An example of such a danger is the presence of another train stopped ahead on the track. Since it is often impossible to stop a train in less than the sight distance, it is desirable for the locomotive engineer to know of the danger before visual contact in order to avoid a problem. While wayside indicators are generally effective in providing this warning, their usefulness may be reduced during periods of fog or other inclement weather.
Since at least the early 1920s, cab signalling has been utilized to supplement discrete wayside indicators. Indicators located in the cab provide the locomotive engineer with continuous signalling information similar to that provided by the wayside indicators.
Cab signalling systems generally operate using a receiver on the locomotive inductively coupled to the track. Specifically, a pick-up coil on the locomotive senses the presence of a modulated alternating current caused by a corresponding potential applied across the track. While modulated in a manner corresponding to the aspects of the wayside indicators, the frequency of the modulated cab signalling carrier is necessarily higher than the modulation frequency to provide effective inductive coupling to the pick-up coil. It has also been necessary to mount the pick-up coils relatively close to the rails, such as on a supporting structure depending from the locomotive.
This present method of mounting pick-up coils on a structure beneath the locomotive has been found to have several disadvantages. The supporting structure itself, for example, is generally not always furnished with the locomotive, and it may be necessary to attach it later when the cab signalling system is installed. This may add significant costs to the cab signalling system. Further, the support structure is of limited utility since it has no other purpose than to maintain the coils in position near the rails. Additionally, pick-up coils mounted close to the rails may be subject to damage by debris encountered on the track. Damage to the pick-up coil and its supporting structure may often be the only damage incurred by a locomotive passing over such debris. Some pick-up coils mounted in this manner may also be somewhat unreliable since vibration of the locomotice can have a tendency to loosen the supporting structure and its associated pick-up coil.
The typical locomotive in service today is of the diesel-electric variety. Mechanical energy provided by an on-board diesel engine is converted via a generator into electrical energy to drive electric traction motors. The electric traction motors then drive the axle. The diesel-electric configuration is preferred because, unlike a diesel engine, an electric motor is capable of operating over a wide operational range without a gear changing transmission. An electric motor may also have greater torque at low speeds than a diesel engine. This greater torque can give the locomotive the ability to start with heavier loads than would otherwise be possible.
The electric traction motor is generally mounted beneath the locomotive adjacent the drive axle. A pinion gear attached to the traction motor shaft engages a drive gear mounted on the axle. Due to irregularities in the respective height of the rails at different points along the track, it is inevitable that the axle will tend to pitch around an axis transverse to the axle and longitudinal to the body of the locomotive. Because it is undesirable that the the locomotive body pitch with the axle, a suspension system is provided to isolate the locomotive body from the axle assembly. Thus, the locomotive body and the axle can have some relative movement. If the traction motor were mounted directly to the locomotive body it would be difficult for the pinion gear to maintain close mesh with the drive gear. In order to maintain this close mesh, the traction motor is mounted directly to the axle. Since the axle must rotate, however, and the traction motor must remain stationary, traction motor support bearings are provided to allow axle rotation.
Since a locomotive traction motor typically weighs at least a ton, failure of a support bearing is undesirable. Thus, the traction motor support bearing is an important component in the operation of the locomotive. The support bearing is often kept continuously lubricated by a felt wick lubricator which is immersed in an oil bath.
Occasionally, dirt or other foreign substances can work under the bearing, causing it to fail. In order to reduce the presence of such foreign substances, a bearing dust guard is utilized around the axle to cover the gap between the bearing and adjacent wheel hub.